Under a Natural Stream Channel and Wetland Design, Assessment, & Monitoring contract for the Philadelphia Water Department, NTM Engineering was part of the GTS Technologies team that assessed streams within the Poquessing Creek Watershed. The resulting report described the watershed with its land use, geology, and soil characteristics and geographic information systems (GIS) maps detailing the multiple sub-watersheds, land use, geology, and soils.
To implement the stream assessment, the team utilized cross-section surveys, cross-section extension surveys, Unified Stream Assessment Method (USAM) worksheets, photographs, longitudinal profiles, bankfull calibrations, pebble counts, Mecklenburg worksheets, sinuosity calculations, canopy covers, infrastructure track downs, narrative descriptions, and GIS mapping.
The Poquessing Creek Watershed Stream Assessment included the sub-watershed reaches.
The team compared the field observed bankfull elevations (from 2007 and 2012) and resulting discharge developed utilizing the Manning’s equation with two other hydrologic sources, including a regional curve for urban areas and the Poquessing Creek Act 167 Plan discharges. USAM results were summarized to describe in-stream habitat, vegetative protection, bank erosion, floodplain connection, buffer condition, vegetated buffer width, and floodplain vegetation, habitat, and encroachment. The team utilizes this information to develop the “best fit” discharge at each cross-section. The team also analyzed the Poquessing Creek Stream Gage discharges using David Rosgen’s “Step Wise Procedure for Calibrating Bankfull Discharge at USGS Stream Gage Stations.” Based on historic land use data, the stream gage rating was compared to land use development over time to demonstrate how the increase in impervious surface affected the stream’s hydrograph and bankfull frequency.
The design team developed detailed recommendations that addressed channel stability and infrastructure and habitat and ranked the recommendations based on channel instability, habitat availability, floodplain connection, threatened infrastructure, and riparian buffer quality to prioritize restoration reaches. The rankings were also mapped to provide a visual aid in restoration planning.
NTM performed GIS, field streambank assessment, and hydrologic and hydraulic (H&H) tasks for this stream assessment project.